Effect of pomegranate (Punica granatum L.) peel and green coffee bean (Coffea arabica) extracts and their formulations on the oxidative stability of raw walnut oil under accelerated oxidation conditions

Abstract This study evaluated the thermal oxidation stability of unrefined walnut oil ( Juglans regia L.) by using methanol extracts from oven-dried ( PE, GE ) and lyophilised ( PL, GL ) pomegranate peel ( Punica granatum L.), oil-free green coffee beans ( Coffea arabica ), and their combinations over 18 days at 60 °C. Extracts’s antioxidant effects were compared with those of gallic acid, alpha-tocopherol, butylated hydroxytoluene, and a control group. Anthocyanin (55.11 mg/100 g), phenolics, DPPH radical scavenging activity (84.06 %), and Trolox equivalent antioxidant capacity (761.60 μg TE /mg) were highest in PL , while ferric ion reducing antioxidant capacity (447.43 μg TE /mg) and ABTS radical scavenging activity (341.85 μmol TE /g) were highest in the PL-GL formulation. ANOVA results indicated that the antioxidants, storage times and their interaction significantly influenced the oil’s quality properties ( P < 0.01 ). PL-GL , PE-GE , PL , and PE extracts can be used to prevent oxidation as alternatives to synthetic options.